<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style type="text/css">
        img:first-child{opacity: 1}
        img:nth-child(2){opacity: 0.8}
        img:nth-child(3){opacity: 0.6}
        img:last-child{opacity: 0.2}
    </style>
</head>
<body>
<div class="demo">
    <img src="icon_cf1b905.png">
    <img src="icon_cf1b905.png">
    <img src="icon_cf1b905.png">
    <img src="icon_cf1b905.png">

</div>
</body>
</html>